This invention relates to apparatus for forming blown films, and more particularly apparatus for forming blown films capable of stabilizing bubbles, and enabling high speed film forming as well as a high blow-up ratio, thereby to form at high efficiencies films highly transparent and having uniform thickness.
Heretofore, a blown film has been formed by extruding a molten resin through a die having a circular slit and blowing air into a cylindrical film thus formed to bulge or inflate the same.
It has been also known in the art to cool the cylindrical film extruded through the die by an air ring disposed near the die.
The prior art apparatus described above cannot be used for high speed forming and high blow-up forming because it cannot sufficiently stabilize the bubbles.
With such prior art apparatus it has been extremely difficult to form blown films by using thermoplastic synthetic resins having a low tension under molten state, such as high density polyethylenes having a density of at least 0.94 and linear low density polyethylenes, etc. calling attentions in recent years.